1. Field of the Invention
The present invention relates to a method of preparing vegetable or fruit juices.
2. Description of the Prior Art
It is well known that vegetable juices and fruit juices are prepared by resorting to ultrafiltration (hereinafter abbreviated as "UF") and reverse osmosis (hereinafter abbreviated as "RO"). The squeezed fluid or extract is clarified by UF and concentrated primarily by RO.
The juice thus treated is very clear and retains the original taste, fragrance and color of the raw material free of degradation. The juice has the further feature that any of the taste, fragrance or color is selectively removable from the juice using a particular kind of membrane. These membrane filtration processes, however, have a common drawback. The filter membrane for UF or RO becomes clogged up thereby resulting in a reduced filtration rate or variations in filtration characteristics such as the molecular weight of the resulting fraction and sodium chloride removal ratio. The impaired performance of the membrane due to its contamination fails to realize the desired intended quality in respect of taste, fragrance, Brix, pigment content, etc. all owing to the variations in the membrane characteristics.
Accordingly, when the contamination of the membrane proceeds, there arises a need to discontinue the production for cleaning of the membrane, which entails a considerable time loss and a reduction in operation efficiency. Various devices have therefore been proposed, for example, for cleaning filter membranes with ease.